The major goal of this project is to understand how metabolic networks are regulated in response to sudden changes in the concentration of environmental nutrients. While we have a good understanding of central carbon metabolism in various steady states, it is unclear how these metabolic networks adapt to maintain viability on timescales that are too short to alter the composition of the proteome. We focus on how the first step in glycolysis is regulated when cells growing slowly on ethanol are exposed to high enough glucose concentrations to induce the high flux through glycolysis that supports rapid, fermentative growth. Starting glycolysis too fast can deplete ATP and kill cells. Preliminary studies suggest that polymerization of a metabolic enzyme plays a crucial role in regulating the kinetics of this transition. We have found that Glucokinase-1 (Glk1), one of the three enzymes responsible for catalyzing the first step in glycolysis, forms linear polymers when respiring cells encounter high glucose concentrations. Purified Glk1 forms polymers in the presence of glucose and ATP and polymerization inhibits Glk1's catalytic activity. Using genetics, we have demonstrated that deleting GLK1 reduces cell death but slows the acceleration of growth rate when respiring cells encounter glucose. Taking advantage of the conservation of glycolysis across all kingdoms of life, we will investigate the way that starved Saccharomyces cerevisiae's metabolism responds to sudden introduction into glucose-rich media as a tractable model for the general response to rapid increases in the environmental glucose concentration. We will tackle this problem at multiple scales: using a combination of genetics, biochemistry and microscopy to understand how Glk1 and its polymerization affect both glycolysis and cellular growth; using a combination of biochemistry and structural biology in order to elucidate how Glk1 polymerization reduces Glk1 enzymatic activity; and determining the conservation of these mechanisms.